Recently, the ongoing development of information industry demands a technology of transmitting large-scale data of various types at high speed. To this end, many ongoing efforts are made to research and develop DAS for the solution to the shadow region problem and the coverage extension by means of a plurality of distributed antennas provided within a conventional cell.
Distributed antenna system (hereinafter abbreviate DAS) is the system that utilizes a plurality of distributed antennas connected with a single base station via wired or dedicated circuit. In this case, the single base station manages a plurality of antennas situated within a cell managed by the base station in a manner of being spaced apart from each other over a predetermined distance. Considering the fact that a plurality of the antennas are distributed and situated within the cell in a manner of being spaced from each other over the predetermined space, the distributed antenna system is discriminated from a centralized antenna system (hereinafter abbreviated CAS). The CAS includes such a cellular communication system as WCDMA (wideband code division multiple access), HSPA (high speed packet data), LTE/LTE-A (long term evolution/long term evolution-advanced) and 802.16. And, the CAS is the system that uses such a multi-antenna scheme as OL-MIMO (open loop-multi input multi output), CL-SU-MIMO (close loop-single user-multi input multi output), CL-MU-MIMO (close loop-multi user-multi input multi output), Multi-BS-MIMO (multi-base station-multi input multi output) and the like in a manner of installing multiple antennas on a single base station in a cell based structure.
The DAS may differ from a femto cell in that a base station at a cell center controls and manages all distributed antenna areas situated within a cell instead of enabling each unit of distributed antennas to control and manage an area of the corresponding antenna. Considering the fact that the distributed antenna units are connected via the wired or dedicated circuit, the DAS may differ from a multi-hop relay system or an ad-hoc network in which a base station and a remote station (RS) are connected by wireless. Moreover, considering the fact that the distributed antennas are able to transmit different signals to user equipments adjacent to the corresponding antennas, respectively, the DAS is discriminated from a repeater that amplifies and transmits a signal only.
Considering that distributed antennas are able to support a single mobile station or multiple mobile stations by transceiving different data stream at the same time, the DAS may be considered as a sort of a multiple input multiple output (MIMO) system. In aspect of MIMO system, the DAS may provide an effect of reducing transmission power owing to the antennas distributed to various locations within a cell in a manner that a transmission area of each antenna is reduced smaller than that of the CAS. Moreover, the DAS enables fast data transmission by decreasing a path loss through a reduction of a transmission distance between an antenna and a user equipment, thereby raising transmission capacity and power efficiency of a cellular system. And, the DAS may satisfy a communication performance quality relatively more uniform that that of the CAS irrespective of a user's location within a cell. Moreover, since a base station is connected with a plurality of distributed antennas via the wired or dedicated circuit, the DAS has small signal loss and lowered inter-antenna correlation and interference to provide a high signal to interference plus noise ratio (SINR).
Thus, the DAS reduces the costs for base station expansion and backhaul network maintenance in a next generation mobile communication system and extends a service coverage, and enhances channel capacity and SINR, thereby becoming a new base of a cellular communications together with the conventional CAS or by being substituted for the CAS.